The present invention relates to polymer alloys required to have chemical resistance, heat resistance and a breaking extension higher than a given level. Particularly, it relates to polymer alloys suitable for battery cases mounted on electric cars and parts of anti-freeze systems for cars.
Conventional battery cases mounted on cars are mainly made of metals. However, with increase of weight, those which are made of plastics are put on the market from the viewpoints of chemical resistance (rust prevention) and insulation properties, and, especially, many of the battery cases are made of plastics mainly composed of crystalline polypropylene (crystalline PP) from the viewpoints of weight-saving and resistance to storage battery electrolytes (resistance to inorganic chemicals).
However, crystalline PP per se is inferior in heat resistance to other polar plastics. Therefore, addition of inorganic fillers such as glass fibers can be considered, but addition of the inorganic fillers causes increase of flexural modulus (rigidity) and decrease of elongation (decrease of pressure resistance) and, in addition, decrease of impact resistance (toughness) and moldability (fluidity). Furthermore, glass fibers which are general inorganic fillers for crystalline PP are weak against alkaline chemicals and are not necessarily suitable as fillers.
Under the circumstances, it is proposed in JP-B-8-5998 to blend crystalline PP with polyphenylene ether (PPE) excellent in heat resistance and impact resistance (especially at low temperatures) (see Comparative Example 1).
However, considering the mounting of batteries (storage batteries) on electric cars, etc. in the future, further improvement of heat resistance, high-temperature rigidity (flexural modulus) and impact resistance will be demanded. In this case, if blending ratio of PPE to the crystalline PP is increased, heat resistance is improved to some extent, but fluidity lowers (injection molding being difficult). Further-more, it has been found that if the blending ratio of PPE is increased, uniform dispersion becomes difficult and, as a result, stable mechanical properties cannot be obtained and problems are caused in chemical resistance (acid resistance, alkali resistance).
In view of the above problems, the object of the present invention is to provide a polymer alloy comprising crystalline PP and PPE which can be improved in heat resistance, high-temperature rigidity and impact resistance without increasing the blending ratio of PPE and which is excellent in moldability (fluidity of materials).
The polymer alloy of the present invention solves the above problems by employing the following constitution.
That is, the polymer alloy of the present invention comprises a crystalline polypropylene, a polyphenylene ether and a syndiotactic polystyrene, wherein the polyphenylene ether is finely dispersed in the crystalline polypropylene and the syndiotactic polystyrene is dispersed in the polyphenylene ether.
The polymer alloy of the present invention preferably contains 2-41 wt % of the syndiotactic polystyrene.
Moreover, the polymer alloy of the present invention comprises a crystalline polypropylene, a polyphenylene ether and a syndiotactic polystyrene, and molded products made from the polymer alloy have a heat distortion temperature (ASTM D 790) of 105xc2x0 C. or higher and a high-temperature flexural modulus (ASTM D 790: 80xc2x0C.) of 1000 MPa or higher.
In addition, the molded products preferably have a high-temperature flexural strength (ASTM D 790: 80xc2x0C.) of 29 MPa or more and, besides, an Izod impact strength (ASTM D 256: 23xc2x0C.) of 300 J/m or more.
The polymer alloy of the present invention usually comprises 34-57 wt % of a crystalline polypropylene, 25-41 wt % of a polyphenylene ether and 2-41 wt % of a syndiotactic polystyrene, the weight ratio of the crystalline polypropylene/polyphenylene ether being 2/1-1/1.